L’alfabeto degli odori

Anna Menini

Neurobiology Sector

International School for Advanced Studies

Trieste, Italy

XC N

cyanide

S HX

thiol

N H 2X

amine

B rX

Halides

Common Odor Compounds

formiates

XO Halcohols

C O O HX

carboxylic acids

X R

O

aldehydes

XO H

O

X H

O

ketones

estersX R

OR

Xalkanes

What is a transduction process?

A transduction process is how the energy of an external

stimulus is converted into an electrical signal

Sensory cells convert a stimulus into an electrical response by a

process known as SENSORY TRANSDUCTION

• 1- IONOTROPIC

2- METABOTROPIC

How many mechanisms of transduction?

C

l

RG

Na+ Ca2+

Ca2+Na

Lightmolecules

Receptor potential=Generator potential

• The change in membrane potential produced by the stimulus is a graded potential and can be:

• positive or depolarizing

• negative or hyperpolarizing

Sensory receptor cells

• Some sensory receptor cells have axons and generate action potentials

• Other cells do not generate action potentials

Scanning electron micrograph of the olfactory epithelium

E. Morrison and R. Costanzo

1m

Morrison and Costanzo 1990

Olfactory transduction takes place in the cilia

R

R

How many odorant receptor genes?

1,000 genes

Nobel Prize in Physiologyor Medicine 2004

• “for their discoveries of odorant receptors and the organization of the olfactory system”

Linda Buck

Richard Axel

1000 recettori

350 recettori

How many type of odorant receptor per cell?

1 type only

How are odorant receptors spatially expressed in the

olfactory epithelium?

Randomly in each of four zones

How many odorant molecules can activate an olfactory sensory

neuron ?

One neuron can respond to many odorant molecules

One type of odorant molecule: how many types of odorant

receptors can activate?

One type of odorant molecule can activate many types of

odorant receptors

PERA

BANANA

Denis

A P B N O C D U G I R F P

DA IN

P U F

P O RD

B UA P

NA U

B N IC

Denis

From olfactory epithelium to olfactory bulb

Representation of olfactory information

Mori et al., 1999

Zonal Organization in the Olfactory System

GLOMERULI

Un certo odore attiva una definita combinazione di glomeruli

NASO BULBO

Information coding in the olfactory cortex

BulbEpithelium Cortex

NASO BULBO CORTECCIA

Olfactory transduction cAMP is

the main second messenger

Ca concentration increases in the ciliaand has a dual effect

1- excitatory2- inhibitory

Ca excitatory effect:direct activation of Cl current

In situ Cl gradient measurements (rat, mucus/knob concentrations)

[Cl-]i = 69 mM[Cl-]o = 55 mM

Ecl = +6mV(Reuter et al.)

Adaptation

Adaptation

• Adaptation adjusts the dynamic range of the response to allow the sensory cell to respond to changes in odor concentration over a wide range.

Mechanism of adaptation

• Intracellular Calcium concentration controls adaptation acting on the transduction cascade

Transduction in an olfactory sensory neuron

Caged compound

Uncaged:physiologically active

8-Bromo-cAMP

1- is resistant to hydrolysis by PDE

2- activates cAMP-gated channels with higher affinity than cAMP

Transduction in an olfactory sensory neuron

S.I.S.S.A. Trieste

Collaborators

C.N.R. GenovaCristiana PiccoPaola Gavazzo

S.I.S.S.A. TriesteLaura LagostenaAnna BoccaccioAndrea MazzatentaGiulietta PinatoSimone PifferiRanken Shimazaki

JapanTakashi Kurahashi

GermanyBenjamin Kaupp

USAStuart FiresteinPeter Mombaerts